Shear-pin system for logging truck bunk

Abstract

Embodiments of a log bunk shear-pin system are shown and described, each embodiment including a shear-pin that engages a log bunk and prevents the bunk from swiveling when the truck is being loaded or unloaded, but that releases the bunk when the shear-pin is mistakenly left engaged during travel. The shear-pin shears, or otherwise comes apart, when the power of the log load or the turning tractor forces the bunk to swivel relative to the tractor or trailer. The preferred shear-pin comprises a shoulder pin and a pin cap connected with a threaded insert. When the forces of a swiveling bunk push on the pin cap and the shoulder pin sideways in opposite directions, the insert breaks. A new insert may then be easily installed into the undamaged pin cap and shoulder pin. Thus, the shear-pin prevents damage to the bunk-ears and only allows damage of an inexpensive and replaceable portion of the shear-pin.

I claim: 
     
       1. A shear-pin system for a logging truck tractor or trailer, the shear-pin system comprising a log bunk system and a, shear-pin, wherein the log bunk system comprises: a bunk for receiving logs and a bridge for being connected to a tractor or trailer, the bunk having a substantially horizontal crossbar connected to the bridge so that the bunk may swivel relative to the bridge with the cross-bar rotating in a horizontal plane,   bunk-ear connected to the bunk, and   bunk-ear connected to the bridge, wherein each bunk-ear has a hole and the bunk-ear boles are aligned when the bunk is generally perpendicular to the tractor or trailer     wherein the shear-pin is received in the aligned bunk-ear holes for restraining movement of the bunk relative to the bridge during loading and unloading of logs, and   wherein the shear-pin comprises: a pin cap having a head portion and a shaft portion extending downwardly from the head portion, the shaft portion having a bottom end and a shaft open interior space extending from the bottom end of the shaft portion up into the shaft portion,   an elongated shoulder pin having a top end and having a shoulder pin open interior space extending from the top end down into the shoulder pin,   an insert having a first end received in binding relationship inside the shaft open interior space and having a second end received in binding relationship inside the shoulder pin open interior space to removably connect the pin cap to the shoulder pin,   wherein opposite sideways forces placed on the pin cap and the shoulder pin by the bunk-ears, caused by road travel of the logging truck, will separate the pin cap and the shoulder pin by breaking the insert.     
     
     
       2. A shear-pin system as set forth in claim 1, wherein the shaft portion has a shaft interior surface defining the shaft open interior space and the insert has an exterior surface, and wherein the said shaft interior surface and the said exterior surface of the insert are threaded for cooperating to removably bind the insert into the shaft interior space. 
     
     
       3. A shear-pin system as set forth in claim 1, wherein the shoulder pin has a shoulder pin interior surface defining the shoulder pin open interior space and the insert has a further exterior surface, and wherein the said shoulder pin interior surface and the said further exterior surface are threaded for cooperating to removably bind the insert into the shoulder pin interior space. 
     
     
       4. A shear-pin system as set forth in claim 1, wherein the insert is made of brass. 
     
     
       5. A shear-pin system as set forth in claim 1, wherein the insert is made of ultra-high-molecular-weight (UHMW) plastic.